This invention relates to pyroelectric devices. In particular, the present invention relates to use of parylene C polymer film for pyroelectric devices.
Pyroelectric detectors are a class of thermal detectors which utilize an electrically poled pyroelectric material. When the pyroelectric material is subjected to a change in temperature, the electrical polarization of the material changes, thereby producing a voltage across the pyroelectric material. In other words, the pyroelectric detector can be characterized essentially as a capacitor upon which a time varying charge, and consequently a voltage, appears when the temperature of the detector is changed. Since the pyroelectric effect is a direct result of the temperature dependence of the polarization, it can be used as a means of detecting infrared radiation energy.
Recently, pyroelectric detectors have attracted great attention due to their potential for low cost, medium to high performance, and room temperature operation. Substantial effort has been spent by many researchers to improve the performance of pyroelectric detectors utilizing ferroelectric crystals such as SBN, TGS, LiTaO.sub.3. The state of the art single element pyroelectric detector performance is a D* of about 1.times.10.sup.9 cm Hz.sup.1/2 /W at 10 Hz. Detectors with thickness of about 3 microns have been fabricated from these ferroelectric crystals.
In addition to the ferroelectric crystals, certain organic polymers also exhibit pyroelectric effects. Considerable research effort has been expended in studying polyvinyl chloride, polyvinyl fluoride (PVF), polyvinylidene chloride, polyvinylidene fluoride (PVF.sub.2), polyacrylometide (PAN), polyacrylonitrile, and poly-o-fluorostyrene. Polymer pyroelectric devices are described in the following U.S. Pat. Nos. 3,769,096 by Askin, et al.; 3,772,518 by Mureyama, et al.; 3,794,986 by Mureyama; 3,809,920 by Coen, et al., 3,824,098 by Bergman, Jr., et al.; 3,885,301 by Mureyama; 3,912,830 by Mureyama, et al.; and British Pat. Nos. 1,376,372 and 1,377,891. A technical article describing the pyroelectric properties of PVF.sub.2 is Appl. Phys., 42, 5219 (1971).
Parylene C is a polymer material which has found use as a window for X-ray radiation detectors. The properties of parylene C and related polymers parylene N and M are discussed in a M. A. Spivack, "Mechanical Properties of Very Thin Polymer Films," Rev. Sci., Instru., 43, 985 (1972). Unsupported, thin parylene films have been prepared and are available in thicknesses down to 0.025 microns. They have extremely uniform thickness, are pin-hole free, have high thermal resistance, are highly insulating, and are extremely mechanically rugged. The typical use of the parylene films as windows for X-ray detectors implies that they have the mechanical strength to support significant pressure differences. Despite the studies of parylene polymers, there has been no report of any parylene polymer being electrically poled, or of pyroelectric behavior in any parylene polymer.